1. Field of the Invention
The present invention relates generally to the field of ophthalmics, more particularly to ophthalmic devices, and still more particularly to ophthalmic devices known as intraocular lenses (IOLs).
2. Background Discussion
At the onset it may helpful to the understanding of the present invention to define the terms "phakic" and "aphakic" as relate to human eyes. The term "phakic" is applied to an eye in which the naturals ocular lens--whatever its condition--has not been removed. In contrast, the term "aphakic" is applied to an eye from which the natural ocular lens has--for any reason--been removed. In this regard, a phakic eye is considered a dynamic or active eye because the natural lens is subject to change over time. In contrast, an aphakic eye is considered a static eye because the natural lens has been removed.
Vision in an eye is enabled by the cornea and the natural lens (and/or an implanted IOL) located posterior of the cornea, both or all of which refract light from a viewed image to the retina of the eye.
One serious and relatively common vision problem is reduced or complete loss of sight due to the natural ocular lens becoming cloudy or opaque--a condition referred to as cataract. The formation of cataracts is most often associated with natural bodily aging processes--perhaps caused or aggravated by long-term exposure to ultraviolet rays from the sun. In any case, most individuals over the age of about 60 years suffer from cataracts at least to some extent.
The current state of ophthalmics, as far as is known to the present inventor, is that cataracts cannot be cured or reversed, nor can the cataract formation process be significantly arrested. Consequently, when a natural lens becomes so cloudy by cataracts (or by any other mechanism) that the lens can no longer effectively refract light from a viewed image to the retina, thereby significantly impairing vision, the corrective action involves the surgical removal of the natural lens. In this manner, a phakic eye becomes an aphakic eye.
After the defective natural lens has been surgically removed, the common current practice is to implant in the individual's aphakic eye an artificial lens called an intraocular lens or IOL. Previously, thick, high diopter spectacles were prescribed for aphakic eyes, such spectacles however being generally disliked by most patients for obvious reasons.
Intraocular lenses are constructed from bio-compatable optical materials and are, to the extent possible, configured to provide the optical characteristics (with the current exception of accommodation) of the removed natural lens in its prior healthy condition.
IOLs are generally considered to have become practical as a result of the World War II discovery by Dr. Peter Ridley that shards of damaged British fighter aircraft canopies made of PERSPEX (i.e., PLEXIGLAS)--an optically clear, hard poly-methyl methacrylate (PMMA) plastic material--embedded in pilots'eyes caused no adverse reaction in the eyes.
As a result of this discovery, hard, rigid IOLs were constructed from an optical grade of PMMA. These rigid IOLs were compatible with then-current surgical procedures used for removing natural lenses in one piece. That is, the PMMA IOLs could be implanted through the relatively large, 5-6 mm, ocular incisions made for removal of the natural lenses.
Subsequently in the early 1970's Dr. Charles Kelman developed a lens-removal procedure utilizing ultrasound to break up natural lenses. This enabled the natural lenses to be extracted with an irrigating fluid in an emulsified condition from the eye through a much smaller ocular incision than that previously needed to extract the natural lens in one piece. This advantageously resulted in reduced patient trauma and patient recovery time.
This new surgical procedure, called phacoemulsification, created a need for elastically-deformable IOLs that could be rolled or folded for insertion into the eye through the same small ocular incision used in the phacoemulsification lens removal procedure, and which then unfolded to their original shape once in the eye. Such deformable IOLs are commonly constructed from an optically clear, high refractive index, biocompatable silicone or acrylic material.
In addition to the implanting of IOLs in aphakic eyes to restore vision after removal of the natural lens, there has recently been an interest in implanting IOLs in phakic eyes to correct vision deficiencies even with healthy natural lenses. The implanting of IOLs in phakic eyes is an often-attractive alternative to some individuals to the wearing of corrective spectacles or contact lenses or having such corneal surgical procedures as radial keratomy (RK) or photo-radialkeratectomy (PRK) performed.
In an aphakic eyes, an IOL is now most commonly implanted in the posterior chamber of the eye in the general location from which the natural lens was removed. Nevertheless, the implanting of an IOL in the anterior chamber is sometimes necessary because, for example, of damage to the posterior wall of the capsular bag during removal of the natural lens. In contrast, an IOL for a phakic eye is most commonly implanted in the anterior chamber of the eye, but may sometimes be implanted in the posterior chamber or on top of the natural crystaline lens.
Regardless of the reason for the implanting of an IOL or the location of the implanted IOL, a principal objective of the present invention is to provide an IOL system in which corrections to IOL spherical, cylindrical and/or add power can be easily made with minimal invasive action.